In the wireless communication system, power control is a key technology. Minimizing the interference in the wireless communication system, on the condition that communication quality is not affected, can be achieved by controlling the transmit power of each User Equipment (UE) and Base Station (BS or eNB), thereby maximizing the system capacity. In addition, the power control further enables the user equipment to have longer standby time.
At present, the power control including opening and closing loops is carried out at the user equipment. Based on such power control, the user equipment needs to transmit a power headroom report to the base station, and based on the received power headroom report, the base station derives a Power Spectral Density (PSD) used by a Physical Uplink Shared Channel (PUSCH) at the user equipment, and the remaining power headroom. Next, with the derived power spectral density and the remaining power headroom, the base station can determine how many Resource Units (RUs) can be allocated to the user equipment and a Modulation and Coding Scheme (MCS) adapted to be used by the user equipment to guarantee obtaining an expected Signal to Interference plus Noise Ratio (SINR) on wireless links between the user equipment and the base station.
In the Third Generation Partnership Project (3GPP) Long Term Evolution (LTE), the aforesaid power headroom is defined as a difference between the allowed maximum transmit power of the user equipment and the current transmit power for PUSCH. In LTE-A, since multiple Carrier Components (CCs) are introduced, new features appear, such as supporting the power control specific to the carrier components, the simultaneous transmission of a Physical Uplink Control Channel (PUCCH) and the PUSCH, and one or more power amplifiers. Thus, the user equipment transmitting power headroom reports to the base station becomes complex compared with LTE-Release 8, and currently, there is no power headroom report considering the new introduced features.
In addition, RAN1 under the Third Generation Partnership Project has agreed to carry out PUCCH and PUSCH power control specific to each carrier component, wherein the PUSCH power control formula for compensating the path loss due to frequency separation is as follows:Pi=min{PCiMAX, 10 log10MPUSCH(i)+PO—PUSCH(i)+αi·(PLi−FPL(Δfi))+FPL(Δfi)+ΔTF(i)+f(Δi)}  (1),
where                PCiMAX is the maximum transmit power of a user equipment on the ith carrier component;        MPUSCH(i) is the number of resource units allocated to the ith carrier component;        P0—PUSCH(i) and αi are open loop power control parameters specific to the ith carrier component;        PLi is the estimated path loss for the ith carrier component;        FPL(Δfi) is the path loss difference due to the frequency separation Δfi for the ith carrier component relative to the anchor carrier component;        ΔTF(i) is the offset with respect to the transport format;        f(Δi) is the function of the closed loop power control command.        
The full compensation for the PUCCH can be calculated via the following formula:PPUCCH(i)=P0—PUCCH(i)+PL(i)+h(·)+ΔF—PUCCH(·)+g(i)  (2)
where                P0—PUCCH(i) is the sum of the cell specific parameter and the user equipment specific parameter specific to the ith carrier component;        PL(i) is the estimated path loss for the ith carrier component;        h(·) is the PUCCH format related parameter;        ΔF—PUCCH(·) is the parameter corresponding to the PUCCH format 1a;        g(i) is the function of the closed loop power control command on the ith carrier component.        
In RAN1#55bis, in addition to the Time Division Multiplexing (TDM) between PUSCH and PUCCH that is currently done in LTE Release8, LTE Release10 also supports simultaneous transmission of PUCCH and PUSCH on the same carrier component. Thus, the transmit power of the user equipment needs to be shared between the two channels so that the total transmit power on the ith carrier component equals to the sum of the transmit power of two channels, i.e. PUSCH and PUCCH, as expressed by the formula below:Pisum=PiPUSCH+PiPUCCH  (3)
where Pisum is the total transmit power of the user equipment on the ith carrier component; PiPUSCH is the transmit power of the PUSCH on the ith carrier component; and PiPUCCH is the transmit power of the PUCCH on the ith carrier component.
Based on the above formula (3), many existing technical solutions related to the power headroom report submit that since the base station knows the standardized rule used to allocate power between PUSCH and PUCCH, they propose to transmit to the base station the power headroom report calculated via the formula below:PiH=Pi,CMAX−PiPUSCH−PiPUCCH  (4)
where PiH is the power headroom on the ith carrier component; and Pi,CMAX is the maximum allowed transmit power on the ith carrier component. However, the power spectral density derived at the user equipment is not only based on the open loop power control but also based on the closed loop power control command function, and the closed loop power control command transmitted by the base station may be incorrect (e.g. when decoding the closed loop power control command at the user equipment, an error occurs or the closed loop power control command signal cannot be detected correctly). Thus, in the existing technical solutions, since the base station only receives the power headroom report including the final power headroom value and does not receive the power value used by the PUSCH and PUCCH on the ith carrier component, it is impossible for the base station to derive the power spectral density used by the PUSCH at the user equipment, and the remaining power headroom, and further it is impossible to accurately determine how many resource units need to be allocated to the carrier component, and thereby it is impossible to achieve accurate resource scheduling and allocating.
Thus, methods and devices for transmitting and receiving a power headroom report are needed to provide a complete power headroom reporting mechanism for the multiple new features (e.g. multiple carrier components, the simultaneous transmission of PUCCH and PUSCH on one carrier component, and one or more power amplifiers) introduced in LTE-A. Based on the power headroom reporting mechanism, the base station may effectively carry out resource allocating and scheduling to achieve the expected transmission quality.